<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>style5</title>
<script src="js/vue.min.js"></script>
<style>
.active {
  width: 100px;
  height: 100px;
  background: green;
}
.text-danger {
  background: red;
}
</style>
</head>
<body>
<div id="app">
  <div v-bind:class="[activeClass, errorClass]"></div>
</div>

<script>
new Vue({
  el: '#app',
  data: {
    activeClass: 'active',
    errorClass: 'text-danger'
  }
})
</script>
</body>
</html>